6,370 research outputs found
Comparison of multi-scale analysis models applied to zonal flow generation in ion-temperature-gradient mode turbulence
During the past years the understanding of the multi-scale interaction
problems have increased significantly. However, at present there exists a range
of different analytical models for investigating multi-scale interactions and
hardly any specific comparisons have been performed among these models. In this
work, two different models for the generation of zonal flows from
ion-temperature-gradient (ITG) background turbulence are discussed and
compared. The methods used is the coherent mode coupling model and the wave
kinetic equation model (WKE). It is shown that the two models give
qualitatively the same results even though the assumption on the spectral
difference is used in the (WKE) approach.Comment: 17 pages, 6 figure
Mean sheared flow and parallel ion motion effects on zonal flow generation in ion-temperature-gradient mode turbulence
The present work investigates the direct interaction of sheared mean flow
with zonal flows (ZF) and the effect of parallel ion motion on ZF generation in
ion-temperature-gradient (ITG) background turbulence. An analytical model for
the direct interaction of sheared mean flows with zonal flows is constructed.
The model used for the toroidal ITG driven mode is based on the equations for
ion continuity, ion temperature and parallel ion motion whereas the ZF
evolution is described by the vorticity equation. The behavior of the ZF growth
rate and real frequency is examined for typical tokamak parameters. It is shown
that in general the zonal flow growth rate is suppressed by the presence of a
sheared mean flow. In addition, with parallel ion motion effects the ZFs become
more oscillatory for increasing value.Comment: 22 pages and 6 figure
Exploring Vacuum Structure around Identity-Based Solutions
We explore the vacuum structure in bosonic open string field theory expanded
around an identity-based solution parameterized by . Analyzing the
expanded theory using level truncation approximation up to level 20, we find
that the theory has the tachyon vacuum solution for . We also find
that, at , there exists an unstable vacuum solution in the expanded
theory and the solution is expected to be the perturbative open string vacuum.
These results reasonably support the expectation that the identity-based
solution is a trivial pure gauge configuration for , but it can be
regarded as the tachyon vacuum solution at .Comment: 12 pages, 5 figures; new numerical data up to level (20,60) included;
Contribution to the proceedings of "Second International Conference on String
Field Theory and Related Aspects" (Steklov Mathematical Institute, Moscow,
Russia, April 12-19, 2009
Regularization of identity based solution in string field theory
We demonstrate that an Erler-Schnabl type solution in cubic string field
theory can be naturally interpreted as a gauge invariant regularization of an
identity based solution. We consider a solution which interpolates between an
identity based solution and ordinary Erler-Schnabl one. Two gauge invariant
quantities, the classical action and the closed string tadpole, are evaluated
for finite value of the gauge parameter. It is explicitly checked that both of
them are independent of the gauge parameter.Comment: 9 pages, minor typos corrected and references adde
Statistical description of turbulent transport for flux driven toroidal plasmas
A novel methodology to analyze non-Gaussian probability distribution
functions (PDFs) of intermittent turbulent transport in global full-f
gyrokinetic simulations is presented. In this work, the Auto-Regressive
Integrated Moving Average (ARIMA) model is applied to time series data of
intermittent turbulent heat transport to separate noise and oscillatory trends,
allowing for the extraction of non-Gaussian features of the PDFs. It was shown
that non-Gaussian tails of the PDFs from first principles based gyrokinetic
simulations agree with an analytical estimation based on a two fluid model.Comment: arXiv admin note: text overlap with arXiv:1008.321
Phase Separation in A-site Ordered Perovskite Manganite LaBaMnO Probed by La and Mn NMR
La- and Mn-NMR spectra demonstrate that the ground state of
the A-site ordered perovskite manganite LaBaMnO is a spatial mixture of
the ferromagnetic (FM) and antiferromagnetic (AFI(CE)) regions, which are
assigned to the metallic and the insulating charge ordered state, respectively.
This exotic coexisting state appears below 200 K via a first-order-like
formation of the AFI(CE) state inside the FM one. Mn spin-spin relaxation rate
indicates that the FM region coexisting with the AFI(CE) one in LaBaMnO
is identical to the bulk FM phase of the disordered form
LaBaMnO in spite of the absence of A-site disorder. This
suggests mesoscopic rather than nanoscopic nature of FM region in
LaBaMnO\@.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
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